Transcript Cavity Monitors

Cavity BPMs for Happex and
G0
John Musson
Triplet Configuration…X, Y, and I
• TM010 Mode for I
• TM110 Mode for X & Y
– Slugs provide proper
excitation, reducing
TM010 x-talk
– Nominal output:
54nV-uA/um (-132
dBm)…per MAFIA
simulations
Cavity Response
___________________
Courtesy Jürgen Schreiber, ECFA/DESY LC workshop, Amsterdam, April 1-4, 2003
I & Q Demodulation
70 MHz
LO
ADC
IQ
DEMO
D
ADC
=
+
0
1
2
3
RE
G
I @ 28 Msps
0
1
2
3
RE
G
Q @ 28
Msps
1
56 Msps System
Clock 14-Bit 2’s
Complement
+
1
COUNTE
R
56 Msps
ADC
90 Degree I &
Q
70 MHz
LO
+I +Q -I -Q +I +Q -I -Q +I +Q -I -Q +I +Q -I -Q +I +Q -I -Q +I +Q
Receiver
Functional Description
Receiver Parameters
• Noise Floor: -91 dBm (200 uV)
– 3690 uA-um per shot (per cavity simulation)
• Bandwidth = 100 kHz
• Processing Gain = 6MSPS/100 kHz = 18 dB
• Best-case Resolution at 50 uA ~ 9 um (at full
BW)
• Additional Integration Gain (16ms): 32 dB
• DAC Output BW ~ 75 kHz (200 ksps)
• Calculated resolution for Eff = 50 %: 0.7 um
– Hoping for 1 um
EPICS Interface
BCM Linearity
Happex Run
Helicity-correlated position
differences, vs stripline,1nm
BCM DD
Resolution
BCM Crosstalk
Glitches
Same plot, better data!
Helicity-correlated position difference.
xtalk
Happex Run
Bad News…..
• Limited Dynamic Range
– Required external amps and filters
• Crosstalk…~45 dB of C-C isolation
– BCM signal would corrupt X & Y
• Software Problems
– Register overflow resulted in glitching and “Bedposts”
• Synchronous Detection => Dedicated MO
– Phase noise and distribution issues (“LOL”)
Data COURTESY l. Kaufman, K. Paschke, R. Michaels
In Addition
• Setup is a learned behavior!
– We devised a procedure, which proved to be
more difficult than expected with actual beam.
• Hall personnel eagerly participated…..
– More eyes
– Technical understanding of benefits and
limitations
– Fantastic model for future systems
G0 Improvements
• Hardware
– Crosstalk path identified. IF “traps” installed on Local Oscillator
lines => > 60 dB
– Amplifier removed from BCM (I) channel
– Additional bench testing to understand
• Software
– Register rollover identified, corrected, and tested.
• MO
– Try asynchronous operation, due to large Phase Noise in Halls
• Hall personnel also system-savvy!
– Data courtesy R. Suleiman
Non-Linear Behavior
“Double Bounce” at Zero X-ing
Glitching
Known Improvements
• 50 nA Sensitivity
– Currently have 74 mm resolution! Need additional 37 dB to achieve 1
mm. LNA?
– I-cavity is not a problem…plenty of signal
•
•
•
•
Shore up all hardware fixes (ie. LO-IF traps)
Firmware and Additional tests.
Setup Procedure (EPICS) and All-Save
Return to Synchronous MO
– Must improve MO Distribution to Hall(s)
• Cavity Investigation on Downstream X&Y
– How can we duplicate beam+cavity behavior in the lab?
• Thank you to all for data, feedback, and especially patience!
CORDIC Algorithm
• COordinate Rotation DIgital Computer
–
–
Jack E. Volder, The CORDIC Trigonometric Computing Technique, IRE Transactions on
Electronic Computers, September 1959
Ray Andraka, A Survey of CORDIC Algorithms for FPGA Based Computers, FPGA '98.
Proceedings of the 1998 ACM/SIGDA sixth international symposium on Field programmable
gate arrays, Feb. 22-24, 1998, Monterey, CA. pp191-200.
• Iterative method for determining
magnitude and phase angle
– Avoids multiplication and division
• Nbits+1 clock cycles per sample
• Can also be used for vectoring and linear
functions (eg. y = mx + b)
Concept
• Exploits the similarity
o
o
between 45 , 22.5 ,
o
11.125 , etc. and
Arctan of 0.5, 0.25,
0.125, etc.
• Multiplies are reduced
to shift-and-add
operations
 cos  sin  
x' , y'  x, y 


sin

cos



Angle
Tan ( )
Nearest
2-N
Atan ( )
45
1.0
1
45
22.5
0.414
0.5
26.6
11.25
0.199
0.25
14.04
5.625
0.095
0.125
7.13
2.8125
0.049
0.0625
3.58
1.406125
0.0246
0.03125
1.79
0.703125
0.0123
0.01563
0.90


 K y  x  d  2 
xi 1  K i xi  yi  di  2i
yi 1
i
i
i
i
i
Functionally.....
Y
Binary search, linked to sgn(Y)
 1, if yi  0
di  
 1, if yi  0
Successively add angles to produce
unique angle vector
   d i  arctan( 2 i )
i
zi 1  zi  d i  arctan( 2 i )
X
Resultant lies on X (real) axis
with a residual gain of 1.6